A bar code is in wide use because it can be read quickly and correctly. Bar codes indicating the information of commodity management, production management, and the like are attached to various articles. The bar code is classified into a one-dimensional bar code having information arranged in one direction and a two-dimensional bar code having information arranged in longitudinal and widthwise directions so that two-dimensional bar code has a larger amount of information than the one-dimensional bar code. The one-dimensional bar code has been mainly attached to commercially distributed commodities and the like having a small amount of necessary information. On the other hand, the two-dimensional code has an advantage of allowing a large amount of information to be accommodated in a small space, and in addition, owing to recent progress of portable telephones and the like, individuals can read and recognize the two-dimensional code easily. Therefore the two-dimensional code has spread rapidly and is utilized by attaching it to information magazines and pamphlets or displaying it on screens. As information to be stored, text information, Internet address information, and the like are listed.
As the two-dimensional code, Code49 (Intermec Technologies Corporation (United States of America)), PDF417 (Symbol Technologies Inc. (United States of America)), Vericode (VERITEC Inc. (United States of America)), DataMatrix (I.D.MATRIX Inc. (United States of America)), QR code (Denso Corporation (Japan)), and the like have been developed and introduced. Of the above-described two-dimensional codes, the Code49, the PDE417, and the like have conventional bar codes stacked one upon another and are called a stack-type two-dimensional code. On the other hand, the QR code, the VeriCode, the DataMatrix, and the like have the form of checkers and are called a matrix-type two-dimensional code. Of these two-dimensional codes, the QR (Quick Response) code developed and introduced by Denso Corporation has been spread and utilized most widely in Japan (see patent document 1).
The minimum unit (black and white square) constituting the QR code is called a cell. The QR code is indicated by the combination of cells and constructed of a position detection pattern (positioning symbol), format information having information such as a timing pattern, an error correction level, and a mask number, data, and an error correction code (Reed-Solomon Code). To indicate the same amount of information, the QR code uses 1/30 of a space used by existing bar codes. Further owing to three positioning symbols, the QR code can be read at any angles in 360 degrees. The positioning symbols means three (one in micro QR) position detection patterns disposed at three corners of the QR code. By retrieving this pattern, it is possible to recognize the position of the QR code, which enables a high-speed read. When 30% of the area of a data region becomes dirty or is lost, the data of the QR code can be restored and identified. Data for restoring the data which has become dirty or has been lost has the effect of preventing erroneous read and preventing erroneous data from being outputted.
The two-dimensional code such as the QR code has more information amount than the one-dimensional bar code. But in a code size which can be recognized by a camera of a portable telephone or the like, the information capacity of the two-dimensional code is as small as the address information of the Internet and is incapable of storing information of a large capacity such as a long sentence of a text and an image. To cope with such a problem and increase the capacity of the two-dimensional code, for example, as a display color of two-dimensional code data, a color two-dimensional code using “white”, “black”, “red”, “green”, and “blue” is disclosed (see patent document 2).
But the color two-dimensional code disclosed in the patent document 2 has a problem that there is a limitation in the data capacity because it has a small number of colors. Further because the colors of cells are judged from the surface of the two-dimensional code to obtain the data of the colors of cells, the data value of each cell merely increases according to an increase of the number of colors. Thus it is impossible to expect a large increase in the data capacity.
Patent document 1: Pat. No. 2,938,338
Patent document 2: Japanese Patent Application Laid-Open No. 2004-234318